<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box {
            background: yellow;
            width: 100px;
            height: 100px;
            position: relative;
            top: 50%;
            left: 50%;
            transform: translate(-50%, -50%);
        }
    </style>
</head>
<body>
    <div style="background-color: aqua; width: 800px; height: 800px;">
        <div class="box">

        </div>
    </div>
</body>
</html>